Butcher's relaxed into G&S role at last (7)
I believe the answer is:
glimpse
'butcher's' is the definition.
(butcher's [hook] is rhyming slang for a look)
'relaxed into gs role at last' is the wordplay.
'relaxed' becomes 'limp' (**).
'into' means one lot of letters goes inside another.
'at last' suggests the final letters.
The final letter of 'role' is 'e'.
'limp' inserted into 'gs' is 'glimps'.
'glimps'+'e'='GLIMPSE'
(Other definitions for glimpse that I've seen before include "Quick view" , "Just a fleeting sighting" , "Gander" , "Catch brief sight of" , "Notice" .)